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Published online by Cambridge University Press: 07 January 2025
Model selection (MS) and model averaging (MA) are two popular approaches when many candidate models exist. Theoretically, the estimation risk of an oracle MA is not larger than that of an oracle MS because the former is more flexible, but a foundational issue is this: Does MA offer a substantial improvement over MS? Recently, seminal work by Peng and Yang (2022) has answered this question under nested models with linear orthonormal series expansion. In the current paper, we further respond to this question under linear nested regression models. A more general nested framework, heteroscedastic and autocorrelated random errors, and sparse coefficients are allowed in the current paper, giving a scenario that is more common in practice. A remarkable implication is that MS can be significantly improved by MA under certain conditions. In addition, we further compare MA techniques with different weight sets. Simulation studies illustrate the theoretical findings in a variety of settings.
We thank the Editor (Peter C.B. Phillips), the Co-Editor (Liangjun Su), two anonymous referees, Jingfu Peng, Yundong Tu, and Yuhong Yang for many constructive comments and suggestions. Xu’s research was partially supported by the National Natural Science Foundation of China (12101591). Zhang’s research was partially supported by the National Natural Science Foundation of China (71925007, 72091212, and 71988101), Beijing Natural Science Foundation (Z240004), and the CAS Project for Young Scientists in Basic Research (YSBR-008).